1. Field of the Invention
This invention relates to a rail wheel. This invention more particularly relates to a new steel for a rail wheel. The invention is particularly concerned with a rail wheel of a steel which is substantially free of abrasion martensite and is characterized by a tensile strength of at least 900 N/mm.sup.2 and a yield point of at least 650 N/mm.sup.2, which rail wheel has a high resistance to rupture and a good abrasion resistance. This invention is also directed to a rail wheel of a steel containing components of bainitic structure.
2. Discussion of the Prior Art
Rail wheels for use on rail vehicles have long been known. Rail wheels heretofore employed are predominantly produced from unalloyed carbon steels. They are used in the naturally hard, normalized, heat-treated and tread heat-treated state. The rail wheel as a solid wheel can consist of one and the same steel or it can take the form of a composite material comprising a high-carbon material for the rail wheel rim interconnected with a softer carbon steel interior thereof which would form the wheel disc and/or wheel hub. Such a composite rail wheel is disclosed in U.S. Pat. No. 1,149,267.
High-carbon wheel rims have a structure which is more or less finely laminated pearlite. This structure and the chemical composition of the wheel rim impair the tenacity of the rail wheel. To such factor there must also be considered the abrasion martensite by block breaking or by slipping and sliding owing to the high carbon content of the steel. The high martensite hardness which results can lead to an acute danger of cracking the rail wheel.
In order to raise the tenacity in the rail wheel rim or in the entire rail wheel, it has been proposed to employ alloyed steels. With these alloyed steels, heat treatments consisting of hardening and tempering have been employed to provide the high tenacities. Even if a bainitic structure is produced by carefully adjusting the analysis by taking into account the given shape of the rail wheel and this is tempered in order to improve tenacity properties, the upper surface of the rail wheel is susceptible to damage by virtue of the abrasion martensite which is not removed by this treatment.
When the stress is very high, e.g., in high velocity rail traffic, considerable risks remain, as the resistance to rupture is inadequate because of the insufficient tenacity and the danger of formation of abrasion martensite.
Accordingly, it became desirable to provide a rail wheel from a steel composition where the rail wheel would be characterized by a high tensile strength of at leaast 900 N/mm.sup.2. Moreover, it became desirable to provide such a rail wheel without expensive heat treatments of highly stressed wheel rims. Still moreover, it became desirable to provide a rail wheel, which rail wheel has a yield point of at least 650 N/mm.sup.2 and had good resistance to rupture and high abrasion resistance. Furthermore, it became desirable to provide such a rail wheel which is not susceptible to the formation of abrasion martensite.